All of a sudden, over at the Leica forum, there is a Nokton f/1 user who said that he thinks the reverse / outward field curvature is mild. I referred him to the tests that Fred Miranda shared in this thread, but then he posted his own FC tests that look like this:
To me, this suggests that there is sample variation at play, and that some lucky buyers may get a lens without the quite noticeable outward field curvature we have seen in images from many users.
Fred, what do you think?
I think the field curvature shape is more extreme at mid-distance. I've tested three copies and they all have the same FC character.
To make any valid observations, aperture and taking distance should be controlled for, from lens to lens. You can either read off the distance scale (rough though it may be) or use a tape measure. Lenses can be expected to be optimised for their 'natural' taking distances, with still decent performance at other distances.
But this one - probably the character of the lens sees it rise above these matters, for most buyers. Almost as part of their brand identity, Cosina lenses have lemon balls and other small quirks. Such design inclusions mark their lenses out as seeking image appeal over and above the pursuit of perfection, as the way to proceed in design. 'Image Firsters' will like that much more than 'Aberration Firsters'.
Yes, it's closer: Focus is set at 2 meters. As I understand it, the FC is zero at infinity and apparently caused by the FLE. This would suggest that FC is present also at 2m. However, it may be more difficult to see in this particular case. In any case, the user claims that it is mild.
grahamgibson wrote:
That's a pretty close focus example. Fred's tests are all at longer distances, so the results could be different.
He posted images like this taken with three lenses: the Apo-Summicron-M, the Nokton f/1 and the re-issue of the Noctilux f/1.2. The FC of the apo look straight and the Noctilux wavy (and not really that sharp + weird OOF behavior). All with focus at 2 meters (on the lens scale) and all wide open.
philip_pj wrote:
To make any valid observations, aperture and taking distance should be controlled for, from lens to lens. You can either read off the distance scale (rough though it may be) or use a tape measure. Lenses can be expected to be optimised for their 'natural' taking distances, with still decent performance at other distances.
But this one - probably the character of the lens sees it rise above these matters, for most buyers. Almost as part of their brand identity, Cosina lenses have lemon balls and other small quirks. Such design inclusions mark their lenses out as seeking image appeal over and above the pursuit of perfection, as the way to proceed in design. 'Image Firsters' will like that much more than 'Aberration Firsters'. ...Show more →
Fred Miranda wrote:
I think the field curvature shape is more extreme at mid-distance or longer. I've tested three copies and they all have the same FC character.
Thanks. Three samples with the same FC behavior suggests that at least most samples are like that. Regarding where the FC is at its strongest, I remember that you posted images taken wide open at infinity, and those appeared to have a flat field. The samples I have seen with the strongest reverse (or outward) FC has been with a focus of several meters, but not near infinity.
However, after checking other users images, I am still speculating that some samples of the Nokton f/1 may have less prominent FC. Here are two more from the Leica forum that at focused at several meters while not showing strong FC, but a rather minor one:
This one has barely visible FC. It's certainly not something I would worry about.
The second image does show some mild reverse FC, but it's not nearly as dramatic as I have seen in other images.
LarsHP wrote:
Thanks. Three samples with the same FC behavior suggests that at least most samples are like that. Regarding where the FC is at its strongest, I remember that you posted images taken wide open at infinity, and those appeared to have a flat field. The samples I have seen with the strongest reverse (or outward) FC has been with a focus of several meters, but not near infinity.
However, after checking other users images, I am still speculating that some samples of the Nokton f/1 may have less prominent FC. Here are two more from the Leica forum that at focused at several meters while not showing strong FC, but a rather minor one:
Your shots made me want to own one some day. Looks awesome. The FC issue is pretty relative, I'm supposed the Noct f1 field curvature wasn't as issue on how it'll be used.
jeffersoncasey wrote:
2 questions - how much crop for the 2nd shot, and other samples showing FC was on other mirrorless body or M bodies (how about yours? I didn't follow this thread closely).
Your shots made me want to own one some day. Looks awesome. The FC issue is pretty relative, I'm supposed the Noct f1 field curvature wasn't as issue on how it'll be used.
These are not my images. I don't have the lens myself, specifically because of the FC behavior.
Regarding the second image in the post above, I think it is the full image. BTW: It appears it was shot at f/1.2 !
I'm pretty sure this is not related to copy variation. You just need the subject distance and background to have the right conditions for the FC to become noticeable.
Fred Miranda wrote:
Amplified field curvature and higher astigmatism for sure.
I have an R5 loaner briefly on hand from CPS and tried most of my M lenses on it (a basic tilted horizon infinity test). But I don't have this VM50/1 to test. In any case, I didn't see any color casts. I don't recall: does the VM50/1 show color cast on some sensors (even on Leica M)? Most of the higher performing lenses IMO are still better on Leica M sensor stack, but I was kind of surprised how usable many would be on the R5. Granted, a lot need f/5.6 or f/8 to clear up across-frame for technical work. I'm also using a relatively cheap Urth adapter and suspect it might not be perfectly flat all the way around.
Fred Miranda wrote:
I think the field curvature shape is more extreme at mid-distance. I've tested three copies and they all have the same FC character.
Are you sure? Your own, excellent field curvature test here and your comment "Notice how the field curvature flattens from close distance towards long distance on the Leica M10-R ..." to that test appears to suggest that the field curvature is at its strongest at close distance (1.5m) and at its flattest at infinity.
rscheffler wrote:
I have an R5 loaner briefly on hand from CPS and tried most of my M lenses on it (a basic tilted horizon infinity test). But I don't have this VM50/1 to test. In any case, I didn't see any color casts. I don't recall: does the VM50/1 show color cast on some sensors (even on Leica M)? Most of the higher performing lenses IMO are still better on Leica M sensor stack, but I was kind of surprised how usable many would be on the R5. Granted, a lot need f/5.6 or f/8 to clear up across-frame for technical work. I'm also using a relatively cheap Urth adapter and suspect it might not be perfectly flat all the way around....Show more →
Regarding color cast / "Italian flag"-issue, I think the backside illuminated sensors (largely) have fixed that. When I tested my Z6UT side-by-side with a Leica M 240, the latter had quite noticeable color change across the frame, while the Z6UT had very little / almost none. This was with the 28mm Summicron Asph II.
LarsHP wrote:
Are you sure? Your own, excellent field curvature test here and your comment "Notice how the field curvature flattens from close distance towards long distance on the Leica M10-R ..." to that test appears to suggest that the field curvature is at its strongest at close distance (1.5m) and at its flattest at infinity.
Yes correct. At long distance (towards infinity), FC flattens when the lens is used on a Leica M body. Field curvature becomes noticeable when focusing a subject at mid-distance while the background is further away. I'm sure you've seen this ill-effect in many images from this lens.
Fred Miranda wrote:
Yes correct. At long distance (towards infinity), FC flattens when the lens is used on a Leica M body. Field curvature becomes noticeable when focusing a subject at mid-distance while the background is further away. I'm sure you've seen this ill-effect in many images from this lens.
I found FC with this lens on the M11 to still have an impact at infinity from f/2 to f/5.6 (weak midframe with sharp center and sharp edges). f/8 or f/11 would help tame it, but it wasn't what I would consider optimal for landscape for edge-to-edge performance, at least not at 60mp and high magnification.
